The present invention relates to a clutch disc applicable to clutch discs for automobiles.
In a conventional type of a friction clutch disc, an annular flange formed integrally with a spline hub has many openings, recesses or the like, which a first torsion spring (for first torsion operation), second torsion springs and third torsion springs engage with, and stop pins pass through. These many openings and recesses are adjacent circumferentially to each other, which may reduce the strength of the flange. Further, the first torsion spring is compressed in the whole torsion area of the clutch disc. In other words, the first torsion spring starts to be compressed before the second and the third springs are compressed, and the maximum compressed length of the first spring is longest and corresponds to a maximum torsion angle of the clutch disc. Therefore, the compression rate of the first spring is very large, and the intended first torsion operation (operation in a small torsion angle area) is hard to obtain when such first springs having a large compression rate.
Accordingly, it is an object of the invention to provide an improved clutch disc, wherein openings for torsion springs are formed in a spline hub flange without reducing strength of the flange. It is another object to provide a clutch disc, wherein the compression rate of a first torsion spring is reduced, a maximum torsion angle is increased, and first hysteresis torque and second hysteresis torque are different in two or more steps of torsion characteristics.